Long-base single-observer range-finder



A. BARR AND w. STROUD.

LONG BASE SINGLE OBSERVER RANGE FINDER. APPLICATION FILED JAN-15,1919- E 33fl25 Patented June 8, 192(1).

2 SHEETS-SHEET I.

I 'J\ 22 W JEQ A. BARR AND W. STROUD.

LONG BASE SINGLE OBSERVER RANGE FINDER.

APPLICATION fILED JAN-15,1919.

1,343,025. Patented June 8, 1920.

2 SHEETS-SHEET 2.

LONG-BASE SINGLE-OBSERVER RANGE-FINDER.

Application filed January 15, 1919.

To all whom it may concern Be it known that we, ARCHIBALD BARR and WILLIAM S'rRoUn, subjects of the King of Great Britain and Ireland, and both of Caxton street, Anniesland, Glasgow, Scot land, have invented new and useful Improvements in Long-Base Single-Observer Range-Finders, of which the following is a specification.

In one type of self-contained-base single observer rangefinder it is customary to have a frame carrying a double telescope supported in the interior of an outer tubular casing which carries doubly reflecting prisms or prism systems one at each end of the base, the frame being geometrically supported, that is in such a way that it is not distorted by external forces applied to the outer casing. For various reasons it is not desirable to make this frame longer than a very few feet. If such a frame, say, 4- feet long be inserted in an outer casing, say, 30 feet long or more, the field of view with any practicable size of end-reflecting prism or system of prisms is necessarily restricted. In other types of single observer rangefinder where the beam of light has to traverse nearly or more than the whole length of the base before entering the double telescope system the restriction of the field is still greater.

This invention relates to self-containedbase single observer rangefinders of the type of instrument which comprises a double telescope system associated with end reflectors, one at each end of the base, and the object of the invention is to provide long base range measuring instruments of this type with means whereby the angular size of the field of View obtainable is increased without impairing the range measuring properties of the instrument, though the intensity of the light is slightly reduced.

According to this invention there is pro vided in combination with one or ea ch of the telescopes of the double telescope system of the instrument and its associated end re flcetor, an optical system in which one real image at least is formed inserted and geometrically supported between the telescope and its end reflector, the magnification of which optical system is fixed and in the plane of triangulation is exactly unity, the optical system or each of them consisting of Specification of Letters Patent.

Patented June 8, 1924),

Serial no. 271,279.

a frame having end lenses, one at each end, at a material distance apart and optical means situated between the end lenses. I

In rangefinders of the general construction referred to above, an optical system according to this invention may be inserted between one of the end reflectors (which in the general construction referred to consist of doubly reflecting prisms) and the objective of its associated telescope, or two optical systems may be provided inserted respectively between. the end reflector and its as sociated objective at each end of the double telescope system. The invention is also applicable to rangefinders of the type where the two beams of light enter the double telescope system both in-the same direction, for instance, to those for use in submarines or under other conditions where an upright disposition of the axis of the instrument is essential. or desirable. In such cases an optical system may be interposed between the upper reflector and its associated objective, so as to obtain from that reflector a more extensive field of view for independent observations when using the instrument 'as a periscope, while the complementary parts of the instrument constituting the rangelinder are out of action.

An optical system for use according to this invention in one form may consist of a tubular frame carrying three convex lenses so arranged that when an object is viewed through it, say, by means of a telescope, the magnification is exactly the same as it is without the system, at all events in one direction, viz., in the plane of triangulation. Further, the aspect must be the same with and without the system in that direction. If this condition is satisfied and the magnification is exactly unity in all directions, the frame supporting the optical system may be moved to a small extent in any possible way without shifting the position of the image seen through it, provided the frame is not so deformed that the relative positions of the lenses forming the system are alter d. It then. such an optical system be inserted between, say, one of the end doubly-rcflecting prisms of a rangefinder and the objective of its associated telescope and be supported in a geometrical manner so that forces applied to the outer casing do not distort the frame carrying the opticalsystem, we shall largely increase the field of view without introducing the possibility of the position of the images being affected by movements of the system as a whole and thus without affecting the rangefinding properties of the instrument. 1

Optical systems of approximately unit magnification have doubtless been used before in optical instruments although so far as we are aware they have not previously been used in connection with rangefinders, but it will be seen that essential features of the present invention, in its application to angle-measuring instruments, are (1) the magnification is fixed and in the plane of triangulation must be very exactly unity, (2) the optical system must be geometrically supported, and the system must be inserted between the parts the separation of which restricts the field.

An optical system particularly suitable for use in carrying out our invention consists in mounting three achromatic objectives of focal lengths FfF in that order upon a frame, the central lens of focal length 7 being at a distance of Qf-l-F from each of the others. Magnification exactly equal to unity may be secured by a delicate adjustment of the position of the central lens. Just as in an ordinary periscope, additional extension of the field of view and of light in the field of view may be secured by placing convex lenses called collector lenses of suitable focal lengths at a distance of 2/ from the central lens one on each side,

6., at the position of the principal focal planes of the lenses whose focal lengths are F.

Although it is an essential. condition of the present invention in its application to rangefinders that the magnification shall be exactly unity in the plane of triangulation, no such restriction exists in the plane perpendicular to this in which we may, 6. 9., by means of astigmaltic lenses produce a magnification greater or less than one, or even negative as, e. 9., if we invert in a plane perpendicular to that of triangulation.

A convenient optical system with lenses alone comprises 3 achromatic lenses, so arranged that the first lens forms an image inverted both vertically and horizontally, the second re-inverts, 2'. 0., makes the image erect while the third produces parallel rays for any point of the image formedby the second.

A modification of the optical system can, however, be produced by reflectors in combination with objectives, 0. 9., a system of fourfold reflection (as in a prismatic binocular) producese an image inverted both vertically and horizontally, so that if such a prismatic system be associated with two achromatic objectives, the first of these objectives may be arranged to erect the image while the second furnishes the parallel rays from any point.

A modification according to this invention consists in the combination of a single reflector with an optical system having two achromatic objectives of equal focal length F separated by a distance 2F. If the com bination be mounted on a frame supported in a geometrical fashion, the reflector being at 45 to the common axis of the lenses, the combination will be equivalent to an ordinary optical square with one roof face 2'. 6., the equivalent of an optical square which produces inversion of the image in the plane perpendicular to that of triangulation. Such an arangement may be used in a long base rai'igefinder to take the place of the ordinary doubly reflecting end reflector.

Some examples of construction and application according to this invent-ion will now be described with reference to the accompanying drawings, in which Figures 1 and 2 are longitudinal sectional elevations illustrating optical systems comprising convex lenses.

Fig. 3 is a longitudinal sectional elevation illustrating an optical system comprising objectives associated with reflectors. Fig. i is an end view and Fig. 5 is a plan of the reflectors.

Fig. 6 is a longitudinal sectional elevation illustrating a modification of the optical system shown at Fig. 3.

Fig. 7 is a longitudinal sectional elevation of an optical system associated with a single, refiector.

Fig. 8 is a view similar to Fig. 7 illustrating a modification of the combination .and Fig. 9 is a cross section of'the reflector taken about the line X Y of Fig. 8.

Figs. 10 and 11 are each longitudinal sectional plan views illustrating long base single observer rangcfin'ders embodying optical systems according to this inventiom Fig. 12 is a sectional elevation and Fig. 13 is a plan illustrating an application of the invention to a rangefinder periscope for submarines.

In the drawings, 1 designates the frame of the optical system. 2 and 3 end achromatic objectives of the system, and 5 or 5 and 6 collector lenses, which need not be achromatic, placed at or near the principal focal planes of the. correspoii'ding objectives.

In Fig. 1, 2 is a lens which brings parallel rays from a distant point to a focus at 7 distant F from lens 2. Rays diverging from 7 form a real image at 8 by means of lens 4. The point 8 is situated at the principal focal plane of lens 3 so that rays diverging from after traversing lens 3 emerge as a parallel beam. The figure shows a perfectly symmetrical system about the center of 4 in which case the magnification is exactly unity; it, however, the two lenses 2 and 3 are not exactly of the same power a slight adjustment of l toward the lens of higher power before the lenses are fixed can be made so as to eilect exact unit magnification.

F 2 differs from Fig. 1 only in the introduction of the collector lenses 5 and 6 placed at the points 7 and 8 respectively of Fig. 1.

Figs. 3, 4 and 5, show an arrangement in which the lens 4: of Fig. 1 is replaced by a fourfold reflector consisting of two right angled reflecting prisms 9 and 10. These prisms need not be cemented together or even touching, nor is it necessary that they should be placed midway between lenses 2 and 3. They may in fact be placed external to the lens system, though of course they must be supported on the same frame. The lenses 2 and 3 should be of equal focal length, equal to halt' the length of the path between 2 and 3 due allowance being made for part or the path being in glass in accordance with well known principles. In this case one real imageis formed midway in the path of the rays.

Fig. 6 corresponds to Fig. 3 except that collector lenses 5 and 5 are shown corresponding in function to lens 5 of Fig. 2.

In Fig. 7, upon frame 1 is mounted a single reflector 11 upon the same frame as lenses 2 and 3 of equal :toeal length. The combination forms a system of unit magnification in the plane of the figure but with the rays turned through 90 from their original direction. The image of a distant object will, however, he inverted perpendicularly to the paper so that in this direction the magnification will be 1. In this case one real image is formed midway between the lenses 2 and 3.

This system may be modified by providing a collector lens introduced as indicat d in dotted lines.

In Figs. 8 and 9, the singly reflecting prism 11 of Fig. 7 is replaced by a prism 12 with root face 13, the effect of which is to introduce an extra inversion perpendicular to the plane of the diagram, so that we have a device which produces unit magnification in every direction but with the rays turned through 90. In this case one r ral image is formed midway between the lenses 2 and 3.

This system may be modified by providing a collector lens 5 introduced as indi- (rated in dotted lines.

Fig. 10 shows a plan view of an ordinary ltorm of rangefinder in which llrep resents the central double telescopic sys tem without details, 15 and 16 the end double reflectors and 17 and 18 optical systoms after the manner of Fig. l inserted as described.

Fig. 11 shows a plan view of a rangefinder in which the end double reflectors are removed and replaced by optical systems which turn the beams through 90, viz., 19 and 20, after the manner of Fig. 7.

ig. 12 shows a sectional elevation and Fi 13 a plan illustrating the application of the invention in the case of a self-contained-base single observer rangefinder having double reflectors 22 and 23, one at each end of its base, for use on board a submarine. When the sea level is at A with only the upper reflector 22 above water the rangefinder is out of action and the instrument is used only as a periscope, but it the submarine rises so that the sea level is represented by B, two views or the target from the two ends of the base are obtained from the reliectors 22 and 23 and the instrument comes into operation as a rangetinder. In the first case when sea level is represented by A, in the absence of the optical system 21, the field of view would be excessively restricted. Any of the optical systems described are suitable for use in instruments of this type.

In Figs. 10, 11, 12 and 13, C designates the outer tubular casing of each instrument and each optical system provided is shown with its frame supported within the outer casing G in a geometrical manner, the method indicated consistsing of a gimbal support D at one position and a bearing support E at another. The bearing support E extends from the frame of the optical system and presents a circular rim which, in the case of Figs. 10 and 11, rests against the interior of the outer casing C which is circular in cross section. in the c mstruction illustrated in Figs. 12 and 13 as the optical system 21 is not concentric with the outer casing "C, concentric sleeves are fixed to the interior of the outer casing within which the optical system is geometrically supported, a sleeve ID being provided for the gimbal D and a sleeve E for the bearing support E. Both the gimbal and bearing supports give freedom of angular movement to the frame in all directions about the axis of the optical system.

We claim:

1. A self-contained-base single observer rangefinder having a double telescope system, a reflector at each end of the base, one for each telescope of the double telescope system, in combination with an optical system in which one real image at least is formed inserted and geometrically sup ported between one of the telescopes and its associated reflector, the magnification of which system is fixed and in the plane of triangulation is exactly unity, the optical system consisting of a frame having end lenses, one at each end, at a material distance apart and optical meanssituated between the end lenses for the purposes set forth.

2. A self-containedbase single observer rangefinder having a double telescope system, a reflector at each end of the base, one for each telescope of the double telescope system, in combination with two optical systems in each of which one real image at least is formed inserted and geometrically supported one between each of the telescopes and its associated reflector, the magnifications of which optical systems are fixed and in the plane of triangulation are exactly unity, each optical system consisting of a frame having end lenses, one at each end, at a material distance apart and optical means situated between the end lenses, for the purposes set forth.

3. A self-contained-base single observer rangefinder having a double telescope system, a reflector at each end of the base, one for each telescope of the double telescope system in combination with an optical system consisting of a frame carrying a central and two end lenses, the end lenses being at a material distance apart, the frame being geometrically supported between one of the telescopes and its associated reflector, the magnification of which system is fixed and in the plane of triangulation is exactly unity, for the purposes set forth.

4:. A self-contained-base single observer rangefinder having a double telescope system, a reflector at each end of the base, one for each telescope of the double telescope system, in combination with an optical system consisting of a frame carrying three achromatic objectives of focal lengths FfF arranged in that order upon the frame, the central lens of focal length f being at a distance of Qf-i-F from each of the others, the system being inserted and the frame geometrically supported between one of the telescopes and its associated reflector, the magnification of which system is fixed and in the plane of triangulation is exactly unity, for the purposes set forth.

5. A self-contained-base single observer rangefinder having a double telescope system, a reflector at each end of the base, one for each telescope of the double telescope system, in combination with an optical sys tem consisting of a frame carrying three achromatic objectives of focal length Ff]? arranged in that order upon the frame, the central lens of focal length 7 being at a distance of 2f+F from each of the others, with collector lenses of suitable focal lengths at a distance of 2f from the central lens, one on each side, the system being inserted with the frame geometrically supported between one of the telescopes and its associated reflector, the magnification of which system in the plane of triangulation is exactly unity, for the purposes set forth.

6. A self-contained-base single observer rangefinder having a double telescope system, a reflector at each end of the base, one for each telescope of the double telescope system, in combination with an optical system in which one real image at least is formed inserted between one of the telescopes and its associated reflector, the magnification of which system is fixed and in the plane of triangulation is exactly unity, said optical system having end lenses at a material distance apart and optical means situated between the end lenses, for the purposesset forth.

7. A self-contained-base single observer rangefinder having a double telescope system, a reflector at each end of the base, one for each telescope of the double telescope system, in combination with two optical systems in each of which the real image at least is formed inserted one between each of the telescopes and its associated objective, the magnification of which optical systems are fixed and in the plane of triangulation are exactly unity, each optical system having end lenses at a material distance apart and optical means situated between the end lenses, for the purposes set forth.

AROHIBALD BARR. WILLIAM STROUD. 

